Power converter

ABSTRACT

A power converter in which the structure of a connecting portion is highly resistant against vibration and has a low inductance. The power converter includes a plurality of capacitors and a laminate made up of a first wide conductor and a second wide conductor joined in a layered form with an insulation sheet interposed between the first and second wide conductors. The laminate comprises a first flat portion including the plurality of capacitors which are supported thereon and electrically connected thereto, a second flat portion continuously extending from the first flat portion while being bent, and connecting portions formed at ends of the first flat portion and the second flat portion and electrically connected to the exterior.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a capacitor module, a power converter,and a vehicle-mounted electrical-mechanical system.

2. Description of the Related Art

Recently, a power semiconductor device capable of switching a largecurrent has been developed. A power converter using such a powersemiconductor device is able to supply electric power to a load, e.g., amotor, with high efficiency through the switching. Therefore, the powersemiconductor device is widely utilized for driving motors ofvehicle-mounted electrical-mechanical systems in trains, automobiles,etc. In a hybrid electric vehicle (HEV), particularly, an engine and anelectric motor are combined with each other to realize outputting ofhigher torque from low rotation speed of the motor, storage ofregenerative energy into a battery, as well as higher fuel economy and areduction of CO₂ in cooperation with an idle stop system (automaticengine stop system).

The power semiconductor device used in the power converter generates aloss at the time of switching. If the switching loss can be reduced, itis possible to reduce heat generated from the power converter, to cutthe number of power semiconductor devices used, and to realize a powerconverter having a smaller size and a higher power density.

To reduce the switching loss, the switching time has to be shortened. Inother words, an effective solution for reducing the switching loss is toincrease a current time-dependent change di/dt and to realize fasterswitching. At the time of switching of a large current, however, ajumping voltage, i.e., an overvoltage in excess of the power supplyvoltage, is caused in the power semiconductor device based on L·di/dt,i.e., based on a abrupt current time-dependent change di/dt and aparasitic inductance L of wiring. Taking into account the jumpingvoltage, the power semiconductor device of the power converter employs adevice that is resistant against a voltage higher than the power supplyvoltage. Reducing the parasitic inductance L of wiring is required tosuppress the jumping voltage and to reduce the loss.

Parts of the power converter, of which inductances are to be reduced,are ones used in a circuit subjected to a momentary current change atthe time of switching, i.e., a smoothing capacitor, a powersemiconductor module using the power semiconductor device, andconductors used for connecting them. In those parts, it is important toreduce a total inductance, including part connecting portions as well.

Known techniques for reducing the inductance of a capacitor aredisclosed in Patent Document 1 (JP,A 2001-268942) and Patent Document 2(JP,A 2004-165309). With those known techniques, the inductance isreduced by arranging a plurality of capacitors on positive and negativeconductors in the form of flat plates, which are opposed to each otherwith insulators interposed between them, and by connecting thecapacitors such that electrodes of adjacent capacitors have differentpolarities, or by connecting a capacitor and a power semiconductormodule in proximity relation so as to shorten the distance between them.

SUMMARY OF THE INVENTION

However, a capacitor module constructed by combining a plurality ofcapacitors with each other is large and weight. Accordingly, when thecapacitors are connected in proximity relation as in the knowntechniques, stresses are concentrated in an electrically connectingportion, thus causing rupture in, e.g., an environment of severetemperature difference within an inverter for the HEV and an environmentof severe vibration encountered when the HEV is driven over a road blockor other level differences in roads. To avoid that problem, it isproposed to interconnect the capacitor module and the powersemiconductor module through a third connecting member for moderation ofthe stresses. Such a solution, however, increases inductance in theconnecting portion and cannot realize a sufficient reduction ofinductance.

Further, a capacitor generates heat due to a ripple current, andtherefore it is required to have a structure suitable for cooling. Inparticular, an inverter for the HEV is usually installed in a closedspace where the environmental temperature in use is 100° C. or higherand cooling based on convection of air within the space is not expected.For that reason, the capacitor is required to have a shape ensuring highthermal conduction and good thermal contact for heat radiation.

In addition, because the capacitors and the power semiconductor moduleare arranged side by side on a plane, the known techniques are notsuitable for satisfying requirements demanded in the inverter for theHEV, i.e., space-saving installation, wiring with a low inductance, anda layered structure in which the capacitors are installed over the powersemiconductor module.

An object of the present invention is to provide a space-savingcapacitor module which has not only a connecting structure ensuring alow inductance and moderation of stresses, but also a structure suitablefor cooling.

To achieve the above object, the capacitor module of the presentinvention is featured in reducing parasitic inductance of connectingportions. The capacitor module comprises a plurality of capacitors; anda laminate electrically connected to the plurality of capacitors andmade up of a first wide conductor and a second wide conductor joined ina layered form with an insulation sheet interposed between the first andsecond wide conductors, the laminate comprising a first flat portionincluding the plurality of capacitors which are supported thereon andelectrically connected thereto; a second flat portion being continuouswith the first flat portion and extending at a large width in adirection away from the plurality of capacitors supported on the firstflat portion; and connecting portions formed at ends of the first flatportion and the second flat portion and electrically connected to theexterior.

Preferably, the first flat portion is resin-molded together with theplurality of capacitors, and the second flat portion is exposed from themolded resin and is extended at a large width in a direction away fromthe molded resin. Further, a bent portion is formed midway the secondflat portion.

Also, the present invention provides a power converter having a smallsize and a high power density, which employs the capacitor moduleconstituted as described above.

More specifically, in a power converter electrically connected between apower supply and a load and controlling transfer of electric powerbetween the power supply and the load, the present invention is featuredin that the capacitor module is electrically connected in parallel tothe power supply side of a power module which includes a powersemiconductor device for switching and is electrically connected betweenthe power supply and the load.

Further, the present invention provides a vehicle-mountedelectrical-mechanical system using the power converter constituted asdescribed above.

More specifically, in a vehicle-mounted electrical-mechanical system forconverting electric power supplied from a vehicle-mounted power supplyinto motive power, the present invention is featured in that the powerconverter is electrically connected between a motor for generating themotive power the vehicle-mounted power supply and the motor and transferof electric power between the vehicle-mounted power supply and themotor.

Thus, according to the present invention, the capacitor module can beobtained which has the connecting structure ensuring a low inductanceand moderation of stresses and which is suitable for reducing a surgevoltage caused at the time of switching in the power converter. Thepower converter having a small size and a high power density can also beobtained by using the capacitor module, and the vehicle-mountedelectrical-mechanical system can further be obtained by using the powerconverter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram of a vehicle equipped with avehicle-mounted electrical-mechanical system according to a firstembodiment of the present invention;

FIG. 2 is a main circuit diagram of a power converter INV used in thevehicle-mounted electrical-mechanical system according to the firstembodiment of the present invention;

FIG. 3 is a perspective view showing an external appearance of acapacitor module CM according to the first embodiment of the presentinvention;

FIGS. 4A and 4B are respectively a sectional view and a partial enlargedview of the capacitor module according to the first embodiment of thepresent invention;

FIG. 5 is an exploded view of the capacitor module according to thefirst embodiment of the present invention;

FIG. 6 is a perspective view of a principal part of the capacitor moduleaccording to the first embodiment of the present invention, the viewincluding arrows for explaining current paths;

FIG. 7 is a side view of a principal part of the capacitor moduleaccording to the first embodiment of the present invention, the viewincluding arrows for explaining current paths;

FIG. 8 is an exploded perspective view showing the connection betweenthe capacitor module CM and a power module PMU of the power converterINV according to the first embodiment of the present invention;

FIG. 9 is a sectional view showing the connection between the capacitormodule CM and the power module PMU of the power converter INV accordingto the first embodiment of the present invention;

FIG. 10 is a plan view of the power module PMU used in the powerconverter INV according to the first embodiment of the presentinvention;

FIG. 11 is an enlarged sectional view of a connecting portion betweenthe capacitor module CM and the power module PMU according to the firstembodiment of the present invention, the view including an arrow forexplaining a current path;

FIG. 12 is an inductance circuit diagram of the power converter INVaccording to the first embodiment of the present invention;

FIG. 13 is a perspective view showing an external appearance of acapacitor module CM according to a second embodiment of the presentinvention;

FIG. 14 is a plan view showing the arrangement of each power module PMUof a power converter INV according to the second embodiment of thepresent invention;

FIG. 15 is an exploded view showing the connection between the capacitormodule CM and the power module PMU of the power converter INV accordingto the second embodiment of the present invention;

FIG. 16 is a perspective view showing a state where the capacitor moduleCM and the power module PMU of the power converter INV according to thesecond embodiment of the present invention are assembled with a drivingcircuit unit DCU and a DC bus bar;

FIGS. 17A and 17B are each a sectional view and an enlarged view showingthe connection between the capacitor module CM and the power module PMUof the power converter INV according to the second embodiment of thepresent invention;

FIG. 18 is a circuit diagram of the power converter INV according to thesecond embodiment of the present invention;

FIG. 19 is a graph roughly showing waveforms of a current and a voltagein one power semiconductor device IGBT of the power converter INVaccording to the second embodiment of the present invention;

FIG. 20 is a sectional view showing the construction of the powerconverter INV according to the second embodiment of the presentinvention;

FIG. 21 is an exploded perspective view showing the construction of acapacitor module according to a third embodiment of the presentinvention;

FIG. 22 is a sectional view showing the construction of a capacitormodule according to a fourth embodiment of the present invention; and

FIG. 23 is a sectional view showing the construction of a capacitormodule according to a fifth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A capacitor module, a power converter, and a vehicle-mountedelectrical-mechanical system according to a first embodiment of thepresent invention will be described below with reference to FIGS. 1-12.

In the following embodiment, a vehicle-mounted power converter isdescribed, by way of example, as the power converter in which isemployed the capacitor module of the present invention.

The construction described below is also applicable to DC-DC powerconverters, such as a DC/DC converter and a DC chopper. Further, theconstruction described below is applicable to power converters used forindustrial and domestic purposes.

FIG. 1 is a block diagram of a hybrid electric vehicle (HEV) in which avehicle-mounted electrical-mechanical system constructed of a powerconverter INV using the capacitor module according to the firstembodiment of the present invention is combined with an internalcombustion engine system.

The HEV to which is applied this first embodiment includes front wheelsFRW and FLW, rear wheels RRW and RLW, a front wheel axle FDS, a rearwheel axle RDS, a differential gear DEF, a transmission T/M, an engineENG, electric motors MG1 and MG2, a power converter INV, a battery BAT,an engine control unit ECU, a transmission control unit TCU, a motorcontrol unit MCU, a battery control unit BCU, and a vehicle-mountedlocal area network LAN.

In this first embodiment, driving forces are generated by the engine ENGand the two motors MG1, MG2 and are transmitted to the front wheels FRWand FLW through the transmission T/M, the differential gear DEF, and thefront wheel axle FDS.

The transmission T/M is constructed by a plurality of gears and iscapable of changing a gear ratio depending on an operating condition,such as speed.

The differential gear DEF is a device for, when there is a speeddifference between the right and left wheels FRW and FLW in a curvedload or the like, distributing motive power to the right and left wheelsFRW and FLW in a proper ratio.

The engine ENG is constructed by a plurality of components, such as aninjector, a throttle valve, an ignition device, and intake and exhaustvalves (all not shown). The injector is a fuel injection valve forcontrolling an amount of fuel injected into a cylinder of the engineENG. The throttle valve is a valve for controlling an amount of airsupplied to the cylinder of the engine ENG. The ignition device is afire source for burning a gas mixture in the cylinder of the engine ENG.The intake and exhaust valves are open/close valves disposed in intakeand exhaust passages for the cylinder of the engine ENG.

The motors MG1 and MG2 are each a three-phase AC synchronous motor,i.e., a permanent-magnet rotary electric machine.

As an alternative, the motors MG1 and MG2 may be each a three-phase ACinductive rotary electric machine or a reluctance rotary electricmachine.

Each of the motors MG1 and MG2 comprises a rotating rotor and a statorgenerating a rotating magnetic field. The rotor is constructed byembedding a plurality of permanent magnets inside a core, or byarranging a plurality of permanent magnets over the outercircumferential surface of a core. The stator is constructed by windingcopper wires around electromagnetic steel plates. By supplying athree-phase AC current to flow through the windings of the stator, therotating magnetic field is generated such that each motor MG1, MG2 canbe rotated by torque generated by the rotor.

The power converter INV controls electric power supplied to the motorsMG1 and MG2 through switching of power semiconductor devices. Brieflyspeaking, the power converter INV controls the motors MG1 and MG2 byestablishing (turning on) or cutting (turning off) the connection of aDC source, i.e., the high-voltage battery BAT, to the motors MG1 andMG2. In this first embodiment, because the motors MG1 and MG2 are each athree-phase AC motor, a three-phase AC voltage is generated inaccordance with duration of a time width of the switching (i.e., an off-and on-duration), to thereby control the driving forces of the motorsMG1 and MG2.

The power converter INV is constituted by a capacitor module CM forsupplying electric power momentarily at the time of switching, a powermodule PMU for performing the switching, a driving circuit unit DCU forsupplying switching power for the power module PMU, and a motor controlunit MCU for deciding the duration of the time width of the switching.

The capacitor module CM and the power module PMU will be described indetail later with reference to FIG. 3 and the subsequent drawings.

The motor control unit MCU decides the switching of the power module PMUso that a rotation speed command n* and a torque command value τ* from ageneral control unit GCU are realized in the motors MG1 and MG2. Inother words, the motor control unit MCU includes a microcomputer and amemory, e.g., a data map, which are required for arithmetic and logicaloperations to decide the switching.

The driving circuit unit DCU drives the power module PMU in accordancewith the switching of the power module PMU, which has been decided bythe motor control unit MCU. To that end, the driving circuit unit DCUincludes a circuit with a driving capability of several amperes (A) andseveral tens voltages (V), which is required to drive the power modulePMU. Also, the driving circuit unit DCU includes a circuit for isolatinga control signal in order to drive power semiconductor devices on thehigher potential side.

The battery BAT is a DC power supply and is constituted by a secondarycell with a high power density, e.g., a nickel hydrogen cell or alithium ion cell. The battery BAT supplies electric power to the motorsMG1 and MG2 through the power converter INV, and also conversely storeselectric power generated by the motors MG1 and MG2 after conversion inthe power converter INV.

The transmission T/M, the engine ENG, the power converter INV, and thebattery BAT are controlled by a transmission control unit TCU, an enginecontrol unit ECU, a motor control unit MCU, and a battery control unitBCU, respectively. Those control units are connected to the generalcontrol unit GCU via the vehicle-mounted local area network LAN with acapability of two-way communication and are supervised in accordancewith command values from the general control unit GCU. Each of thosecontrol units controls corresponding equipment based on, e.g., a commandsignal (command value) from the general control unit GCU, output signals(values of various parameters) from various sensors and the othercontrol units, as well as data and maps which are stored in a storagebeforehand.

For example, the general control unit GCU computes a torque valuerequired for the vehicle depending on an amount by which an acceleratoris depressed in accordance with a driver's acceleration demand, anddistributes the required torque value into an output torque value forthe engine ENG and an output torque value for the first motor MG1 sothat operation efficiency of the engine ENG is increased. Thedistributed output torque value for the engine ENG is transmitted as anengine torque command signal to the engine control unit ECU, and thedistributed output torque value for the first motor MG1 is transmittedas a motor torque command signal to the motor control unit MCU, therebycontrolling the engine ENG and the motor MG1, respectively.

The operation mode of the hybrid electrical vehicle will be describedbelow.

First, when the vehicle starts running or it runs at low speed, themotor MG1 is primarily operated as a motor and the rotational drivingforce generated by the motor MG1 is transmitted to the front wheel axleFDS through the transmission T/M and the differential gear DEF. As aresult, the front wheel axle FDS is rotated by the rotational drivingforce from the motor MG1 to rotate the front wheels FRW and FLW, thusenabling the vehicle to run. At that time, output power (DC power) fromthe battery BAT is supplied to the motor MG1 after conversion intothree-phase AC power by the power converter INV.

Next, during ordinary running of the vehicle (i.e., running at mediumand high speeds), the engine ENG and the motor MG1 are used in acombined manner. More specifically, the rotational driving forcegenerated by the engine ENG and the rotational driving force generatedby the motor MG1 are both transmitted to the front wheel axle FDSthrough the transmission T/M and the differential gear DEF. As a result,the front wheel axle FDS is rotated by the rotational driving forcesfrom the engine ENG and the motor MG1 to rotate the front wheels FRW andFLW, thus enabling the vehicle to run. Also, a part of the rotationaldriving force generated by the engine ENG is supplied to the motor MG2.With such distribution of motive power, the motor MG2 is rotated by thepart of the rotational driving force generated by the engine ENG tooperate as a generator, thus generating electric power. The three-phaseAC power generated by the motor MG2 is supplied to the power converterINV and is rectified to DC power. Thereafter, the DC power is convertedagain into three-phase AC power that is supplied to the motor MG1. As aresult, the motor MG1 generates the rotational driving force.

During acceleration of the vehicle, in particular, during quickacceleration in which the opening of the throttle valve for controllingthe amount of air supplied to the engine ENG is fully opened (e.g., whenthe vehicle is climbing a steep up-slope and the accelerator isdepressed in large amount), output power from the battery BAT issupplied to the motor MG1 after conversion to three-phase AC power bythe power converter INV, in addition to the above-described operationduring ordinary running, thereby increasing the rotational driving forcegenerated by the motor MG1.

During deceleration or braking of the vehicle, the rotational drivingforce of a drive shaft (DSF) generated by the rotation of the frontwheels FRW and FLW is supplied to the motor MG1 through the differentialgear DEF and the transmission T/M, whereby the motor MG1 is operated asa generator to generate electric power. The three-phase AC power(regenerative power) obtained by the power generation is rectified to DCpower by the power converter INV, which is then supplied to the batteryBAT. The battery BAT is thereby charged. When the vehicle is stopped,the driving of the engine ENG and the motors MG1 and MG2 is stopped in abasic mode. However, when a remaining level of the batter BAT is low,the driving of the engine ENG is continued to operate the motor MG2 as agenerator, and the generated electric power is supplied to and chargedin the battery BAT through the power converter INV.

The operations of the motors MG1 and MG2 for the power generation andthe driving are not limited to particular ones. Depending on efficiencydemanded, the motors MG1 and MG2 may be operated to play roles reversalto the above-described ones.

FIG. 2 is a circuit diagram of a main circuit, in which a large currentflows, in the power converter INV for the vehicle-mountedelectrical-mechanical system according to the first embodiment of thepresent invention. Note that, in FIG. 2, the same characters as those inFIG. 1 denote the same parts.

The power converter INV according to this first embodiment isconstituted by the capacitor module CM for supplying electric powermomentarily at the time of switching, the power module PMU forperforming the switching, the driving circuit unit DCU for supplyingswitching power for the power module PMU, and the motor control unit MCUfor controlling the switching waveform to control the motor. While FIG.2 shows the arrangement of the power converter INV for the first motorMG1, the power converter INV in FIG. 1 includes the power module PMU andthe driving circuit unit DCU for the second motor MG2, which have thesame arrangements as those shown in FIG. 2.

The power module PMU constitutes three bridge circuits (Au, Av and Aw)for outputting a three-phase AC current by using power semiconductordevices Mpu, Mnu, Mpv, Mnv, Mpw and Mnw which perform the switching(turning-on and -off).

Opposite ends of each of those bridge circuits are connected toconnecting portions 3 b and 4 b of the capacitor module CM throughconnecting portions 3 a and 4 a which are connected to the respectiveopposite ends of the bridge circuits.

Midpoints of the bridge circuits are connected to three-phase inputconnecting portions (U-, V- and W-connecting portions) of the motor MG1through connecting portions 24U, 24V and 24W, respectively.

The bridge circuits are each a serial circuit which is constituted byconnecting two power semiconductor devices electrically in series perphase, and which is also called an arm. A part of the serial circuitincluding the power semiconductor device which outputs a higherpotential is called an upper arm, and a part thereof including the powersemiconductor device which outputs a lower potential is called a lowerarm.

The power semiconductor devices of the three bridge circuits (Au, Av andAw) are subjected to switching (turning-on and -off) with a phasedifference of 120° to generate the three-phase AC voltage, therebyswitching the connection between the higher potential side (upper arm)and the lower potential side (lower arm). Thus, the three-phase ACvoltage having a pulse voltage waveform different in the duration of thetime width is generated.

To perform the switching of a large current, the power semiconductordevices (Mpu, Mnu, Mpv, Mnv, Mpw and Mnw) require an external drivingsource power for the switching. To that end, the driving circuit unitDCU for driving of the switching is connected to the power module PMU.

Further, the motor control unit MCU is connected to the driving circuitunit DCU to receive signals indicating the motor rotation speed, thetime width and timing (duration of the pulse width) of the switchingdepending on torque, etc. from the motor control unit MCU.

In the illustrated circuit diagram of this first embodiment, IGBT(Insulated Gate Bipolar Transistor) is used as each of the powersemiconductor devices (Mpu, Mnu, Mpv, Mnv, Mpw and Mnw). Therefore,diodes Dpu, Dnu, Dpv, Dnv, Dpw and Dnw adapted for the powersemiconductor devices in which currents are returned at the time ofswitching are each connected between the collector and the emitter ofthe IGBT in anti-parallel arrangement (such that the direction from theemitter toward the collector is a forward direction).

Also, while the power semiconductor device in the upper (lower) arm perphase is constituted by one component (two including the associateddiode) in the illustrated circuit diagram of this first embodiment, aplurality of power semiconductor devices may be connected in paralleldepending on the current capacity demanded.

Further, while IGBT is used as the power semiconductor device in theillustrated circuit diagram of this first embodiment, MOSFET (MetalOxide Semiconductor Field-Effect Transistor) may be used instead. In thecase of MOSFET, since a diode for returning a current is incorporated,there is no need of additionally arranging a diode.

The power module PMU is enclosed by a case, and the power semiconductordevices are mounted on a metal plate, called a base, with an insulatingsubstrate interposed between them. Electrical connections betweensemiconductor chips, between the semiconductor chips and inputterminals, and between the semiconductor chips and output terminals areestablished so as to form a three-phase circuit by connectingconductors, e.g., aluminum wires or plate-like conductors. The base ismade of a thermally conductive material, e.g., copper or aluminum, andserves to cool heating of the power semiconductor devices caused by theswitching. For the cooling, the underside of the base is exposed to acoolant, e.g., air or cooling water. From the viewpoint of increasingthe cooling efficiency, it is preferable to provide fins or the likesfor increasing the contact area with the coolant. The insulatingsubstrate is made of an insulating material with high thermalconductivity, e.g., aluminum nitride. Boundaries between the base andthe insulating substrate and between the insulating substrate and thepower semiconductor devices are bonded by using a bonding material,e.g., a solder.

The power module PMU performs the switching of a large current.Therefore, the power module PMU requires a low-impedance circuit whichis capable of momentarily changing the current at the time of switching.Because the high-voltage battery BAT includes the internal impedance andthe inductance of connecting cables, it has a high impedance and cannotconstitute a low-impedance circuit for the power module PMU.

In view of the above point, the capacitor module CM is installed nearthe power module PMU within the power converter INV and is connected soas to constitute a low-impedance circuit at the time of switching of thepower module PMU. More specifically, assuming that the capacity of acapacitor is C and the frequency is f, the capacitor itself has a lowimpedance of Z=1/(2×π×f×C) at high frequency. However, the parasiticinductance of wirings inside both the capacitor module and the powermodule and the parasitic inductance of connecting portions between thecapacitor module and the power module generate a high impedanceZ=2×π×f×L, wherein L is the parasitic inductance and f is the frequency,at high frequency caused upon the current being changed momentarily.Further, as a current change dI/dt increases, a jumping voltageV=L×dI/dt caused by the parasitic inductance L is also increased.

The capacitor module according to this first embodiment is designed torealize the features that inner wirings have a low inductance, and theconnecting portions between the capacitor module CM and the power modulePMU is constituted as low-inductance connection having a stressmoderating structure. Therefore, the switching of the powersemiconductor module can be sped up (namely, dI/dt can be increased),and the switching time can be shortened. In other words, a time t duringwhich a large current I and a large voltage V cross each other can beshortened and generated heat Q=I×V×t can be held small. With thereduction of the generated heat Q, the temperature of each powersemiconductor device can be lowered and the number of the powersemiconductor devices can be reduced. It is hence possible to realize areduction in size and cost of the power converter.

The capacitor module CM according to the first embodiment of the presentinvention will be described below with reference to FIGS. 3-12.

FIG. 3 is a perspective view showing an external appearance of thecapacitor module CM according to the first embodiment of the presentinvention. The capacitor module CM is covered with a case 12 for resinmolding, and the case 12 has holes 17 which are used for fixing andinclude nuts buried therein. The case 12 has connecting portions 3 c and4 c for connection to the high-voltage battery BAT and connectingportions 3 b and 4 b for connection to the power module PMU. Further, alaminate (described later) of wide conductors 8 and 9, which supportcapacitor cells CDSs and are joined in a layered form with an insulationsheet 10 interposed between them, is withdrawn from the case 12 forresin molding, as it is, to extend up to the outside of molded resin,thereby forming the connecting portions 3 b and 4 b for connection tothe power module PMU.

FIGS. 4A and 4B are respectively a sectional view and a partial enlargedview of the capacitor module according to the first embodiment of thepresent invention.

The capacitor cells CDSs are supported on the laminate of the wideconductors 8 and 9 in the layered form with the insulation sheet 10interposed between them, and they are electrically connected to the wideconductors 8 and 9 at connecting portions formed at one-side ends of thewide conductors 8 and 9. The capacitor cells CDSs and a part of thelaminate are covered with the case 12 having an opening and are moldedwith resin 13. A bent structure for moderating stresses is provided in apart of the laminate (8, 9 and 10), which is not resin-molded, and theconnecting portions 3 b (4 b) for connection to the power module PMU areformed at the other-side ends of the wide conductors 8 and 9.

The resin 13 used for the molding can be any suitable type so long as itis an insulating material with good thermal conductivity and moistureresistance. By forming holes, projections and/or recesses in the layeredwide conductors 8 and 9, adhesion of the wide conductors to the resin isincreased and heat generated from the capacitors are more effectivelytransmitted to the wide conductors, thus resulting in more efficientheat radiation.

The resin-molding case 12 is preferably made of a material havingmoisture resistance and heat resistance, e.g., PPS. By resin-molding thelayered wide conductors 8 and 9, the capacitor module CM is obtained inthe form capped by the resin-molding case 12, and therefore moistureresistance of the capacitor cells CDSs can be increased.

Thus, the resin molding contributes to increasing not only reliabilityat the connecting portions between the capacitor cells CDSs and the wideconductors, but also the cooling capability and moisture resistance as aresult of closer adhesion between the capacitor cells CDSs and the wideconductors.

The bent structure and the effect of reducing inductance and moderatingstresses with the bent structure will be described below with referenceto FIG. 4B which shows a bent portion of the laminate in enlarged scale.

In the structured obtained by bending, into a U-shape, the laminate ofthe wide conductors 8 and 9 in the layered form with the insulationsheet 10 interposed between them, when stresses are applied in thevertical direction and in the left-and-right direction as viewed on thedrawing sheet, those stresses can be moderated. The directions and pathsof currents flowing through the wide conductor 8 and the wide conductor9 are as indicated by 80 and 81, respectively. With the bent structureof the laminate, the currents 80 and 81 flow in directions cancelingeach other and a low inductance is realized in spite of the length ofeach wide conductor being increased with the presence of the bentportion. Stated another way, inductance coupling occurs betweeninductances 67-N and 67-P of the wide conductors 8 and 9 in the bentportion, and resulting inductance can be reduced when the currents 80and 81 flow through the bent portion at the same time.

FIG. 5 is an exploded view of the capacitor module CM according to thefirst embodiment of the present invention.

As shown in FIG. 5, the capacitor cells CDSs constituted by a pluralityof capacitors are arranged inside the resin-molding case 12. In thisfirst embodiment, each capacitor in the capacitor cell CDS is a filmcapacitor obtained through the steps of winding a film which is coatedwith a metal by vapor deposition, and forming electrodes 11 on oppositesurfaces of the wound film in its axial direction by metal spraying.Thus, in the capacitor used in this first embodiment, the electrodes 11are positioned on both the side surfaces in opposed relation.

The laminate of the wide conductor 8, the insulation sheet 10, and thewide conductor 9 is arranged under the capacitor cells CDSs.

The wide conductor 8 has an area allowing the plurality of capacitorcells CDSs to be all supported on it. In other words, when the pluralityof capacitor cells CDSs each having a cylindrical shape are placed sideby side on the wide conductor 8, the wide conductor 8 is formed of aconductor with a width larger than the total width of a capacitorassembly in its longitudinal direction. Raised lugs 14 for connection tothe electrodes 11 of the capacitor cells CDSs are formed on an uppersurface of the wide conductor 8. As shown in FIG. 5, by way of example,when six capacitor cells CDSs are used, six raised lugs 14 are formed.Further, the raised lugs 14 are arranged, as shown, such that a raisedlug 14-A connected to a capacitor cell CDS-A in the most front side asviewed on the drawing sheet is positioned to be capable of beingconnected to the electrode 11 at the left side, as viewed on the drawingsheet, of the capacitor cell CDS-A and a raised lug 14-B connected to acapacitor cell CDS-B in the second most front side as viewed on thedrawing sheet is positioned to be capable of being connected to theelectrode 11 at the right side, as viewed on the drawing sheet, of thecapacitor cell CDS-B. Thus, the raised lugs 14 are arranged in a zigzagpattern.

Similarly to the wide conductor 8, the wide conductor 9 also has an areaallowing the plurality of capacitor cells CDSs to be all supported onit. In other words, when the plurality of capacitor cells CDSs eachhaving a cylindrical shape are placed side by side on the wide conductor9, the wide conductor 9 is formed of a conductor with a width largerthan the total width of a capacitor assembly in its longitudinaldirection. Similarly to the raised lugs 14, raised lugs 15 forconnection to the electrodes 11 of the capacitor cells CDSs are formedon an upper surface of the wide conductor 9. In a state where the wideconductors 8 and 9 are joined in the layered form, the raised lugs 15penetrate through-holes 16 formed in the wide conductor 8 and projectabove the wide conductor 8. As shown in FIG. 5, by way of example, whensix capacitor cells CDSs are used, six raised lugs 15 are formed as withthe raised lugs 14. Further, the raised lugs 15 are arranged, as shown,such that a raised lug 15-A connected to the capacitor cell CDS-A in themost front side is positioned to be capable of being connected to theelectrode 11 at the right side of the capacitor cell CDS-A and a raisedlug 15-B connected to the capacitor cell CDS-B in the second most frontside is positioned to be capable of being connected to the electrode 11at the left side of the capacitor cell CDS-B. Thus, the raised lugs 15are also arranged in a zigzag pattern. Accordingly, looking at onecapacitor cell CDS, the raised lug 14 of the wide conductor 8 isconnected to the electrode 11 on one end surface thereof, and the raisedlug 15 of the wide conductor 9 is connected to the electrode 11 on theother end surface thereof. The plurality of capacitor cells CDSsconstituting the capacitor module CM are connected in parallel withrespect to the wide conductor 8 and the wide conductor 9. The wideconductors 8, 9 and the side-surface electrodes 11 of the capacitorcells CDSs are electrically connected to each other by, e.g., a solder.

The raised lugs 14 and 15 serving as connecting terminals of thecapacitor cells CDSs are formed by cutting parts of the wide conductors8 and 9 and raising the cut parts three-dimensionally (perpendicularly)with respect to the wide conductor surfaces. With the provision of theraised lugs 14 and 15, the capacitor cells CDSs and the wide conductors8, 9 can be connected to each other without using any additionalconnecting members, and the number of points to be soldered can bereduced, thus resulting in a reduction of the number of steps and thecost. In addition, it is possible to improve reliability of theconnecting portions, to reduce electrical resistance thereof, and toincrease heat radiation.

The layered wide conductors 8 and 9 are each made of a copper-basematerial having low resistance and high thermal conductivity. When areduction in weight is demanded, an aluminum-base material is used.Soldering of the aluminum-base material is enabled by plating nickel orlike on the surface of the aluminum-base material. Each of the wideconductors 8 and 9 has a thickness of 1 mm.

The insulation sheet 10 is preferably as thin as possible. When theenvironment temperature inside the power converter is 120° C. atmaximum, the insulation sheet 10 is formed of a sheet of polypropylene(PP) or polyethylene (PET) which has a thickness of not larger than 1mm, e.g., about 0.2 mm or 0.4 mm, which can be easily deformed into adesired shape, and which has good adhesion to the molded resin. Thethinner the insulation sheet 10, the smaller is inductance because thewide conductors 8 and 9 can be more closely positioned to each other inthe layered form. When the power converter INV has a small currentcapacity, the layered wide conductors 8 and 9 may be modified such thatmetals are printed on both sides of the insulation sheet 10 and theprinted metals are used as wide conductors. In that case, anotherconnecting conductor is separately prepared for connection.

Each of the wide conductors 8 and 9 has a first flat portion on which issupported the capacitor cells CDSs, and a second flat portion bentperpendicularly to the first flat portion. Near centers of the secondflat portions of the wide conductors 8 and 9, as shown in FIG. 4,U-shaped bent portions 8 c and 9 c are formed to extend in thelongitudinal direction of the second flat portion. The bent portions 8 cand 9 c serve to moderate stresses caused in the connecting portions.Each of the bent portions is not limited in shape to a U-bent form andmay be of a structure having any of other suitable shapes, such as aV-bent form, so long as it is able to moderate stresses applied to theconnecting portions.

FIG. 6 is a perspective view of a principal part of the capacitor moduleaccording to the first embodiment of the present invention, the viewincluding arrows for explaining current paths

One connecting portion 4 c and three connecting portions 4 b are formedat the end of the wide conductor 8. Also, one connecting portion 3 c andthree connecting portions 3 b are formed at the end of the wideconductor 9. The connecting portions 3 c and 4 c are used for connectionof cables and a bus bar extended from the high-voltage battery BAT. Theconnecting portions 3 b and 4 b are used for connection to the U-phasearm, the V-phase arm, and the W-phase arm of the power module,respectively.

In the connecting portions 3 b and 4 b, screws are inserted from aboveand fastened. Taking into account the necessity of such a screwingoperation, the bent portions 8 c and 9 c are formed to project from thesecond flat portion in a direction reversal to the direction in whichthe connecting portions 3 b and 4 b are projected.

FIG. 6 shows a state where the capacitor cells CDSs are fixedlyconnected onto the laminate of the wide conductor 8, the insulationsheet 10, and the wide conductor 9. The raised lug 15-A of the wideconductor 9 is connected to the electrode 11-A on the right side surfaceof the capacitor cell CDS-A, and the raised lug 14-B of the wideconductor 8 is connected to the electrode 11-B on the right side surfaceof the capacitor cell CDS-B.

By arranging and connecting the capacitor cells CDSs as described above,currents are caused to flow through the laminate in directions cancelingeach other and a low inductance can be realized.

Let here look at currents flowing through the capacitor cells CDS-A andCDS-B, for example.

The current flowing through the capacitor cell CDS-A is indicated by68-A, and the current flowing through the capacitor cell CDS-B isindicated by 68-B. Those two currents flow counterclockwise andclockwise as viewed on the drawing sheet, respectively, i.e., in opposeddirections.

FIG. 7 is a side view of a principal part of the capacitor moduleaccording to the first embodiment of the present invention, the viewincluding arrows for explaining current paths.

The currents 68-A and 68-B shown in FIG. 6 also flow through the wideconductors 8 and 9 in opposed directions. More specifically, thecurrents 68-A and 68-B flow through an inductance 61-A of the wideconductor 8 and an inductance 61-B of the wide conductor 9, which arepositioned just under the capacitor cells CDSs, in opposed directions.Therefore, a low inductance is realized based on inductance coupling.

Further, magnetic fluxes produced by the currents 68-A and 68-B inducecurrents 69-A and 69-B which flow in a direction coming out from thedrawing sheet and in a direction going into the drawing sheet,respectively. Thus, the currents 69-A and 69-B are canceled each otherand a low inductance is realized from this point of view as well.

FIG. 8 is an exploded perspective view showing the connection betweenthe capacitor module CM and the power module PMU of the power converterINV according to the first embodiment of the present invention.

The capacitor module CM shown in the upper side of FIG. 8 is the same asthat described above with reference to FIGS. 3-7. The power module PMUis arranged under the capacitor module CM. The power module PMU has theU-phase arm, the V-phase arm, and the W-phase arm, which have electrodes(4 a-U, 3 a-U, 4 a-V, 3 a-V, 4 a-W and 3 a-W) formed at their oppositeends. Corresponding to such an arrangement, the capacitor module CM ofthis first embodiment has three pairs of connecting portions 4 b and 3b.

Through-holes capable of receiving screws are formed in the connectingportions 3 b and 4 b of the capacitor module CM, and those holes arepositioned in match with the connecting portions 3 a and 4 a of thepower module PMU such that both the modules are electrically andmechanically connected to each other by using screws. Note that thenumber of the connecting portions of the capacitor module CM is ofcourse not limited to three pairs and can be changed depending on thenumber of the connecting portions of the power module PMU.

FIG. 9 is a sectional view showing the connection between the capacitormodule CM and the power module PMU of the power converter INV accordingto the first embodiment of the present invention.

FIG. 10 is a plan view of the power module PMU used in the powerconverter INV according to the first embodiment of the presentinvention.

As shown in FIGS. 9 and 10, the power module PMU includes a copper base20 for cooling, a case 21 bonded to an upper surface of the copper base20 in its outer peripheral portion, an insulating substrate 19 solderedto the upper surface of the copper base 20 near its center, IGBTs (M)and diodes soldered onto circuit patterns of the insulating substrate19, and external connecting conductors 22 withdrawn from the interior ofthe case 21 to the exterior. External connecting conductors 22-Cconstitute six electrodes at the opposite ends of the U-phase arm, theV-phase arm, and the W-phase arm, and their ends serve as the connectingportions (4 a-U, 3 a-U, 4 a-V, 3 a-V, 4 a-W and 3 a-W) for connection tothe capacitor module CM. Also, external connecting conductors 22-Mconstitute electrodes for outputting a three-phase voltage at midpointsof the U-phase arm, the V-phase arm, and the W-phase arm, and their endsserve as the connecting portions (24U, 24V and 24W) for outputting athree-phase AC current to the motor MG1. Electrical connections betweenthe IGBTs (M) and diodes and the external connecting conductors 22-C,between the external connecting conductors 22-M for outputting thethree-phase voltage and the circuit patterns on the insulatingsubstrate, and between the circuit patterns on the insulating substrateare established by a plurality of aluminum wires 18.

In the power module PMU of this first embodiment, the upper arm and thelower arm for each phase are constituted by connecting three pairs ofpower semiconductor devices IGBTs and diodes in parallel. However, thepower module PMU is of course not limited to that arrangement, and thedimension and number of the devices can be of course changed dependingon the current capacity. Also, while this first embodiment employs asingle 6-in-1-module for providing a three-phase output by one module,three 2-in-1-modules each providing a one-phase output by one module maybe arranged side by side. Note that since this embodiment is describedin connection with the connecting portions between the capacitor moduleCM and the power module PMU through which a large current flow, wiringsfor switching the power semiconductor devices (i.e., gate wirings),terminals accessible from the exterior, and wiring patterns are notshown in the drawings.

The connecting structure between the capacitor module CM and the powermodule PMU according to this first embodiment will be described below.

As shown in FIG. 9, a direction in which the connecting portions 3 a and4 a of the power module PMU are extended after being bent (i.e., adirection indicated by E in FIG. 9) and a direction in which theconnecting portions 3 b and 4 b of the capacitor module CM are extendedafter being bent (i.e., a direction indicated by F in FIG. 9) are set tobe the same.

FIG. 11 is an enlarged sectional view of the connecting portion betweenthe capacitor module CM and the power module PMU according to the firstembodiment of the present invention, the view including an arrow forexplaining a current path.

As shown in FIG. 11, the current in the wide conductor 8 flows throughthe connecting portions 4 b and 4 a as indicated by an arrow 22-C.Looking at the current flowing through each of the connecting portions 4b and 4 a, the directions of those currents are opposed to each other,i.e., in canceling relation. Stated another way, the currents in theopposed directions flow through an inductance 62-P in the connectingportion 4 b of the capacitor module CM and an inductance 57-P in theconnecting portion 4 a of the power module PMU, whereby a low inductanceis realized based on inductance coupling.

The above-mentioned three kinds of inductance reducing effects will bedescribed below together with reference to a circuit diagram.

FIG. 12 is an inductance circuit diagram of the power converter INVaccording to the first embodiment of the present invention.

For the purpose of explaining an abruptly changed current and a voltagecaused by the current, the following description is made of primarilyinductance components while resistance components are omitted. Also, forthe power module PMU, only one arm (Au) of U-phase is described and thepower semiconductor devices Mpu and Dpu of the upper arm and the lowerarm are represented by one device.

In FIG. 12, the same characters represent parasitic inductances in thesame parts as those in FIGS. 4, 7 and 11.

A parasitic inductance 53 represents the inductance of cables and a busbar which connect the high-voltage battery BAT and the power converterINV to each other.

A parasitic inductance 55 represents the inductance of cables and a busbar which connect the power converter INV and the motor MG1 to eachother.

A parasitic inductance 54 represents the inductance of a part of thefield winding of the motor MG1.

The power module PMU has not only an inner parasitic inductance 56, butalso parasitic inductances 57-P and 57-N produced in the connectingportions to the power supply on the higher potential side and the lowerpotential side due to the necessity of securing a certain insulationdistance.

The capacitor module CM has parasitic inductances 61-A and 61-B in theplurality of the capacitor cells CDS-A, CDS-B for supplying andabsorbing electric power momentarily and the wide conductors on whichare supported those capacitor cells CDSs, parasitic inductances 67-P and67-N in the layered wide conductors positioned outside the molded resin,and parasitic inductances 62-P and 62-N in the connecting portionsthereof. Note that only two capacitor cells CDS-A and CDS-B areillustrated herein.

Let now consider a current change caused when the power semiconductordevice Mpu in the upper arm of the power module PMU is turned off fromthe on-state. A path through which a current flows upon the powersemiconductor device Mpu in the upper arm being turned on is indicatedby a current path 64. Because the inductances 54 and 55 are large, acurrent flowing through those inductances cannot be quickly changed atthe time of switching. In that turning-off state, therefore, a currentpath 65 passing the power semiconductor device Dnu in the lower arm isestablished. Thus, looking at a circuit in which a current has beenabruptly changed, it is equivalently regarded that the current flowsthrough a current path 66. By reducing the parasitic inductance presentin a closed circuit formed by the current path 66, it is possible toreduce the jumping voltage at the time of switching, and to suppressheating of the power semiconductor device caused by speedup of theswitching. The above description is made in connection with theswitching at which the power semiconductor device Mpu in the upper armis turned off from the on-state. Conversely, when the powersemiconductor device Mpu in the upper arm is turned on from theoff-state, the power semiconductor device Mnu in the lower arm is turnedoff from the on-state and therefore the current also flows through thecurrent path 66 although the direction of the current is reversed.Further, it is similarly understood that, at the time of switching ofthe power semiconductor device Mnu in the lower arm, the current flowsthrough the current path 66 in either the same direction or the reverseddirection.

The first inductance-reducing effect is obtained by the bent structureof the laminate shown in FIG. 4B.

Stresses applied to the connecting portions are moderated by thepresence of the bent structure. Further, in the bent structure, sincethe currents flow through the wide conductors 8 and 9 of the laminate inthe opposed directions, inductance coupling is caused between theinductances 67-P and 67-N so as to reduce a total inductance. In otherwords, the parasitic inductances 67-P and 67-N in FIG. 12 are coupled toeach other, thus resulting in a small inductance.

The second inductance-reducing effect is obtained by the zigzagconnection of the capacitor cells CDSs and the layered wide conductors8, 9 shown in FIG. 7.

As shown in FIG. 7, the currents 68-A and 68-B flowing through the wideconductors 8 and 9 on which are supported the capacitor cells CDS-A andCDS-B are opposed in direction. Thus, since the currents 68-A and 68-Bflow in the opposed directions through the inductance 61-A of the wideconductor 8 and the inductance 61-B of the wide conductor 9 which arepositioned just under the capacitor cells CDS-A and CDS-B, respectively,a low inductance is realized based on inductance coupling. In otherwords, the parasitic inductances 61-A and 61-B shown in FIG. 12 arecoupled to each other, thus resulting in a low inductance.

The third inductance-reducing effect is obtained by the connectionstructure between the capacitor module CM and the power module PMU shownin FIG. 11.

As shown in FIG. 11, the currents flow through the connecting portion 4b of the capacitor module CM and the connecting portion 4 a of the powermodule PMU in the opposed directions canceling each other. Therefore,the inductance 62-P in the connecting portion 4 b of the capacitormodule CM and the inductance 57-N in the connecting portion 4 a of thepower module PMU are coupled to each other, thus resulting in a lowinductance.

As a result, in addition to the moderation of stresses in the connectingportions, a low inductance of the current path 66 in FIG. 12 can also berealized based on the above-mentioned three inductance-reducing effectsby using the capacitor module CM of this first embodiment.

In the past, in an environment of severe temperature difference withinan inverter for the HEV and an environment of severe vibrationencountered when the HEV is driven over a road block or other leveldifferences in roads, the conventional heavy capacitors cannot beconnected in proximity relation. To prevent rupture in an electricalconnecting portion, therefore, a third connecting conductor is oftendisposed between a capacitor module and a power semiconductor module;namely, another low-inductance connecting conductor is often usedbetween the capacitor module CM and the power module PMU. In such acase, two connecting points are required between the capacitor moduleand the connecting conductor and between the connecting conductor andthe power module. An increase in the number of the connecting pointsincreases inductance for the reason that the conductors are brought intoan exposed state due to the necessity of access from the exterior, suchas screwing, and a certain insulation distance is required.

In this first embodiment, since the bent structure is formed in thelaminate extending from the capacitor module CM to realize directconnection between the capacitor module CM and the power module PMU,stresses are moderated and inductance is reduced with a reduction in thenumber of the connecting points. Assuming, for example, that theinsulation distance of 8 mm is required in terms of the creepingdistance in the connecting portion to the power supply with a withstandvoltage of 600 V, elimination of one connecting point can reduceinductance of 8 nH because a distance of 1 mm corresponds to aninductance increase of about 1 nH.

The construction of a capacitor module CM and a power converter INVaccording to a second embodiment of the present invention will bedescribed below with reference to FIGS. 13-20.

This second embodiment enables, in the motor system shown in FIG. 1, thepower converter INV for controlling two motors MG1 and MG2 to berealized with a low inductance, a stress moderating structure and asmaller size.

FIG. 13 is a perspective view showing the construction of each capacitormodule according to the second embodiment of the present invention. FIG.14 is a plan view showing the arrangement of each power module accordingto the second embodiment of the present invention. FIGS. 17A and 17B areeach a sectional view showing the power converter according to thesecond embodiment of the present invention. FIG. 18 is a circuit diagramshowing the entire construction of the power converter INV according tothe second embodiment of the present invention. Note that, in thosedrawings, the same characters as those in FIG. 4-14 denote the sameparts.

A basic construction of each capacitor module CM1, CM2 is the same asthat of the capacitor module CM shown in FIGS. 4-12. This secondembodiment is featured in the following point. As shown in FIG. 13, onecapacitor module CM1 has connecting holes enabling two power modulesPMU1 and PMU2 to be mounted to the capacitor module CM1, and the othercapacitor module CM2 paring with the capacitor module CM1 also hasconnecting holes enabling the two power modules PMU1 and PMU2 to bemounted to the capacitor module CM2. Further, hole positions in theconnecting portions between the capacitor module CM1 and the two powermodules PMU1, PMU2 and hole positions in the connecting portions betweenthe capacitor module CM2 and the two power modules PMU1, PMU2 arematched with each other such that those components can be jointlyconnected together by screwing. In other words, each capacitor moduleCM1, CM2 has the connecting holes in number twice the number of theconnecting holes formed in the capacitor module CM shown in FIG. 4.

FIG. 14 shows the arrangement of each power module PMU of the powerconverter INV according to the second embodiment of the presentinvention. The two power modules PMU1 and PMU2 have the same structureas that shown in FIG. 10. Those power modules PMU1 and PMU2 are arrangedside by side on a plane such that the connecting portions for thecapacitor modules having the same polarity are close to each other. Morespecifically, a W-phase negative connecting portion PMU1-3 a-W of thepower module PMU1 and a U-phase negative connecting portion PMU2-3 a-Uof the power module PMU2 are positioned close to each other, and aW-phase positive connecting portion PMU1-4 a-W of the power module PMU1and a V-phase positive connecting portion PMU2-4 a-V of the power modulePMU2 are positioned close to each other. Thus, the connecting portionsof the two power modules are positioned close to each other per each ofpositive pole and negative pole. Because of the power modules PMU1 andPMU2 having the same construction, when the connecting portions for thecapacitor modules are arranged in oppositely facing relation such thatthe poles having the same polarity are close to each other, a U-phasepositive connecting portion PMU2-4 a-U of the power module PMU2 and aU-phase positive connecting portion PMU1-4 a-U of the power module PMU1are each positioned without oppositely facing the electrode of the powermodule on the opposite side. Accordingly, in the connecting portions ofeach of the capacitor modules CM1 and CM2 for connection to the powermodules, the number of positive poles is larger than the number ofnegative poles by one, as shown in FIG. 13.

FIG. 15 is an exploded view showing the connection between the capacitormodule CM and the power module PMU of the power converter INV accordingto the second embodiment of the present invention.

As shown in FIG. 15, the capacitor modules CM1 and CM2 are connectedrespectively to the two power modules PMU1 and PMU2, of which connectingportions for the capacitor modules are arranged in oppositely facingrelation to the connecting portions of the capacitor modules, byscrewing the oppositely-facing connecting portions from above andjointly fastening them together. More specifically, the connectingportion CM2-4 b-2U of the capacitor module CM2, the connecting portionCM1-4 b-2U of the capacitor module CM1, and the connecting portionPMU2-4 a-U of the power module PMU2 are jointly connected together byone screw. Likewise, the other connecting portions also connected suchthat CM2-3 b-2U, CM1-3 b-2U and PMU2-3 a-U are jointly connectedtogether by one screw, CM2-3 b-1W, CM1-3 b-1W and PMU1-3 a-W are jointlyconnected together by one screw, CM2-4 b-1W, CM1-4 b-1W and PMU1-4 a-Ware jointly connected together by one screw, CM2-4 b-2V, CM1-4 b-2V andPMU2-4 b-V are jointly connected together by one screw, and so on.

FIG. 16 is a perspective view showing a state where the capacitor moduleCM and the power module PMU of the power converter INV according to thesecond embodiment of the present invention are assembled with a drivingcircuit unit DCU and a DC bus bar.

Two driving circuit units DCU1 and DCU2 are arranged on the two powermodules PMU1 and PMU2, and the two capacitor modules CM1 and CM2 areconnected onto the driving circuit units DCU1 and DCU2, respectively.The two capacitor modules CM1 and CM2 are connected to each other by aDC bus bar DC-Bus for applying the voltage of the high-voltage batteryBAT. The DC bus bar DC-Bus is formed by partly overlapping two kinds ofconductors on the high potential side (positive side) and the lowpotential side (negative side) in a layered form with an insulationsheet (not shown) being interposed between them, and it has connectingportions DC-Bus-P and DC-Bus-N for connection to the high-voltagebattery BAT. To prevent noise from spreading to the exterior, commonmode choke filters CF are further mounted between the capacitor modulesCM1, CM2 and the connecting portions DC-Bus-P and DC-Bus-N,respectively. In addition, there are disposed a resistance for urgentdischarge from the capacitor modules CM1 and CM2 when the operation ofthe HEV is stopped, and connecting portions DC-Bus-PR1, DC-Bus-NR1,DC-Bus-PR2, and DC-Bus-NR2 for connection of natural dischargeresistances.

FIGS. 17A and 17B are each a sectional view showing the connectionbetween the capacitor module CM and the power module PMU of the powerconverter INV according to the second embodiment of the presentinvention. The sections shown in FIGS. 17A and 17B represent theposition where the connecting portions PMU1-4 a-W and PMU2-4 a-V of thepower modules PMU1 and PMU2 are close to each other.

The two capacitor modules CM1 and CM2 and the two power modules PMU1 andPMU2 are electrically connected to each other by two screws 23. Withthat connection, one capacitor module is connected onto one powermodule, while ensuring a low inductance, in one pair of the power modulePMU1 and the capacitor module CM1 and the other pair of the power modulePMU2 and the capacitor module CM2.

More specifically, as shown in the enlarged view of FIG. 17B, atransient current 66-A generated upon a shift from the turning-on to-off at the time of switching of the power module PMU1 flows through theconnecting portion CM1-4 b-1W of the capacitor module CM1 and theconnecting portion PMU1-4 a-W of the power module PMU1 in opposeddirections. Therefore, parasitic inductances CM1-62-P and PMU1-57-P inthose connecting portions are coupled to each other and wiring with alow inductance can be realized. Also, a transient current 66-B generatedupon a shift from the turning-on to -off at the time of switching of thepower module PMU2 flows through the connecting portion CM2-4 b-2V of thecapacitor module CM2 and the connecting portion PMU2-4 a-V of the powermodule PMU2 in opposed directions. Therefore, parasitic inductancesCM2-62-P and PMU2-57-P in those connecting portions are coupled to eachother and wiring with a low inductance can be realized.

Further, with the connection structure according to this secondembodiment, even when the transient current generated upon a shift fromthe turning-on to -off at the time of switching of the power module PMU1is going to flow from the connecting portion CM2-4 b-2V of the capacitormodule CM2 to the connecting portion PMU1-4 a-W of the power modulePMU1, the directions of the currents flowing through those connectingportions are not opposed to each other. Therefore, parasitic inductancesCM2-62-P and PMU1-57-P in those connecting portions are not magneticallycoupled to each other and wiring with a low inductance is not realized.Stated another way, the capacitor module CM2 has a larger parasiticinductance than the capacitor module CM1 with respect to the powermodule PMU1, and it exhibits a high impedance for a high-frequencycurrent changed momentarily at the time of switching. As a result, thetransient current generated upon a shift from the turning-on to -off atthe time of switching of the power module PMU1 is suppressed fromflowing into a low-inductance path formed by the power module PMU2 andthe capacitor module CM2.

Likewise, a transient current generated upon a shift from the turning-onto -off at the time of switching of the power module PMU2 is alsosuppressed from flowing into a low-inductance path formed by the powermodule PMU1 and the capacitor module CM1.

Accordingly, even when the power modules PMU1 and PMU2 are subjected tothe switching at the same time, it is possible to prevent an adverseeffect that respective jumping voltages are summed to be doubled up to alevel exceeding the withstand voltage of the power semiconductor device.

On the other hand, the capacitor module CM2 can be regarded as beingconnected to the power module PMU1 in parallel to the capacitor moduleCM1 for supply of a low-frequency current in the turned-on state afterthe switching. Thus, in the turned-on state, a low-frequency current canbe supplied to the power module PMU1 as a current 64-A from thecapacitor module CM1 and a current 64-B from the capacitor module CM2,as shown in the enlarged view of FIG. 17B.

Also, a low-frequency current can be similarly supplied to the powermodule PMU2 from both the capacitor modules CM1 and CM2.

As described above, each capacitor module serves as a proximal capacitorwith low-inductance wiring, which reduces the jumping voltage, for thepower module positioned just below the capacitor module, and also servesas a capacitor, which increases capacity, for the power modulepositioned below the capacitor module in obliquely adjacent relation. Ina power converter having two power modules, therefore, there is no needof additionally arranging an extra capacitor for reducing the jumpingvoltage. Hence, in the motor system shown in FIG. 1, the power converterINV for controlling the two motors MG1 and MG2 can be realized in asmaller size by using the capacitor modules each having a low inductanceand the stress moderating structure.

FIG. 18 is a circuit diagram of the power converter INV according to thesecond embodiment of the present invention.

Specifically, FIG. 18 shows a circuit diagram of the power converterINV, shown in FIGS. 15-17, which is constituted by the two power modulesPMU1 and PMU2 and the two capacitor modules CM1 and CM2 for controllingthe two motors MG1 and MG2.

In the following, parasitic inductances in the jointly-fastenedconnecting portions of the capacitor modules CM1 and CM2 and the powermodules PMU1 and PMU2 are primarily described, while other parasiticinductances are omitted. In the circuit diagram, three-phase arms Au, Avand Aw contained in the power module and constituted by bridge circuitsof power semiconductor devices are displayed in the form of a box.Further, control circuits, such as the driving circuit unit DCU, are notshown. Other identical characters to those in the foregoing drawingsdenote the same parts.

A voltage is applied from the high-voltage battery BAT to the capacitormodules CM1 and CM2 through the DC bus bar DC-bus shown in FIG. 16.Parasitic inductances DC-bus-LP and DC-bus-LN in the circuit diagramrepresent the parasitic inductances of the DC bus bar DC-bus on thehigher potential side (positive side) and the lower potential side(negative side), respectively. The common mode choke filters CF forpreventing noise are disposed in the DC bus bar between the capacitormodules CM1, CM2 and the input connecting portions DC-Bus-P andDC-Bus-N, respectively. In addition, a discharge resistance DR isdisposed in the DC bus bar between the capacitor modules CM1, CM2 andthe common mode choke filters CF.

In the connecting portions between the capacitor module CM1 and thepower module PMU1, there are parasitic inductances CM1-62P and PMU1-57Pon the higher potential side and parasitic inductances CM1-62N andPMU1-57N on the lower potential side, which are magnetically coupled toeach other for each of the higher potential side and the lower potentialside for the current 66-A flowing at the time of switching, therebyrealizing wiring with a low inductance.

Also, in the connecting portions between the capacitor module CM2 andthe power module PMU2, there are parasitic inductances CM2-62P andPMU2-57P on the higher potential side and parasitic inductances CM2-62Nand PMU2-57N on the lower potential side, which are magnetically coupledto each other for each of the higher potential side and the lowerpotential side for the current 66-B flowing at the time of switching,thereby realizing wiring with a low inductance.

On the other hand, looking at a current path 64B bridging thejointly-fastened connecting portions of the two capacitor modules CM1and CM2 and the two power modules PMU1 and PMU2, the parasiticinductances CM2-62P and PMU1-57P in those connecting portions on thehigher potential side are not magnetically coupled to each other in thedirections of the currents flowing through those connecting portions,whereby a low inductance is not resulted. That point is similarlyapplied to the bridging (jointly-fastened) connecting portions on thelower potential side. As a result, the transient currents 66-A and 66-Bgenerated at the time of switching of the power modules PMU1 and PMU2 donot affect each other. For example, assuming the length of oneconnecting portion to be 15 mm, the total length of the two connectingportions on the higher potential side is 30 mm. Assuming an inductanceper 1 mm to be 1 nH, the inductance on the higher potential side(positive side) is 30 nH. The total inductance on both the higherpotential side (positive side) and the lower potential side (negativeside) is 60 nH.

As compared with the inductances in the bridging connecting portions,the parasitic inductance in each of the capacitor modules CM1 and CM2according to this second embodiment can be reduced by an order ofmagnitude. Therefore, the transient current (several gigas A/s)generated at the time of switching hardly flows through the bridgingconnecting portion. In other words, the current path 66-A at the time ofswitching of the power module PMU1 and the current path 66-B at the timeof switching of the power module PMU2 are kept from interfering witheach other. As a result, it is possible to prevent respective jumpingvoltages from being summed to be doubled up to a level exceeding thewithstand voltage of the power semiconductor device.

On the other hand, for a current flowing through the motor MG1 andhaving low frequency f of about several hundreds Hz which is supplied inthe turned-on state after the switching, the inductance L (e.g., 60 nH)in the bridging connecting portion appears as an impedance Z=2×π×f×L,i.e., several μΩ, and therefore it hardly gives resistance. Accordingly,the capacitor module CM2 can be regarded as being connected at a lowimpedance to the power module PMU1 in parallel as with the capacitormodule CM1, and can supply a current. Thus, in the turned-on state, thelow-frequency current can be supplied as the current 64-A from thecapacitor module CM1 and the current 64-B from the capacitor module CM2.

Similarly, the low-frequency current can also be supplied to the powermodule PMU2 from both the capacitor modules CM1 and CM2.

FIG. 19 is a graph roughly showing waveforms of a current and a voltagein one power semiconductor device IGBT of the power converter INVaccording to the second embodiment of the present invention.

As shown in FIG. 19, the current waveform rises quickly (several gigasA/s) at on-switching. After an almost flat current (several hundreds Hz)flows for a period of several microseconds, the current waveform fallsquickly (several gigas A/s) at off-switching.

The current appearing flat in FIG. 19 is in fact a low-frequency currentof several hundreds Hz. Because FIG. 19 shows a span of several tensmicroseconds in enlarged scale, such a current seems flat.

The waveforms of FIG. 19 are assumed to represent the waveforms of theIGBT which constitutes the upper arm of the power module PMU1 in FIG.18. In an on-switching period (TR) of the upper arm of the power modulePMU1, the diode in the lower arm of the power module PMU1 is turned offand a high-frequency recovery current generated at the time ofturning-off of the diode flows through the current path 66-A in thecircuit diagram of FIG. 18. The generation of the recovery currentcauses a through current to flow in the IGBT at a level in excess of thecurrent supplied. During the on-switching period (TR), the voltage ofthe upper arm IGBT is reduced to almost zero (in fact to several voltsdue to a conduction loss) during the on-switching period (TR).Meanwhile, the diode in the lower arm is turned off, whereupon a jumpingvoltage due to a recovery current caused at the turning-off of thatdiode occurs in the diode and the IGBT in the lower arm (waveforms ofthe current and the voltage in that diode being not shown). With thestructure according to this second embodiment, however, since thecurrent path 66-A is formed as a low-inductance circuit, the jumpingvoltage caused in the lower arm by the recovery current flowing throughthat diode can also be reduced.

During a period (TP) in which the upper arm is in the completelyturned-on state, low-frequency currents flow from the capacitor modulesCM1 and CM2 through the current paths 64-A and 64-B in the circuitdiagram of FIG. 18. Because those currents have low frequency of aboutseveral hundreds Hz, the parasitic inductance (30 mH) in the connectingportions of the capacitor modules and the power modules cause noinfluence upon those low-frequency currents. Accordingly, the twocapacitor modules CM1 and CM2 form a parallel circuit in whichsubstantially no impedance is interposed between them, and the currentsflow into the upper arm almost evenly from the two capacitor modules CM1and CM2. Since the turned-on period (TP) is several tens microsecondsand longer than the switching period (TR, TS) of shorter than 1 μs, heatgenerated from the capacitor modules CM1 and CM2 is decided depending onthe amount of the currents flowing during the turned-on period (TP).Thus, with the currents almost evenly supplied from the two capacitormodules CM1 and CM2 during the turned-on period (TP), heat is alsoalmost evenly generated from the two capacitor modules CM1 and CM2,whereby the useful life of each of the capacitor modules CM1 and CM2 isprolonged.

In an off-switching period (TS) of the upper arm, the current flowing inthe power module PMU1 is quickly reduced to zero. As described above,therefore, a high-frequency current flows through the current path 66-Ain the circuit diagram of FIG. 18. Accordingly, a jumping voltage inexcess of the power supply voltage is caused in the upper arm due tosuch a current change, as indicated by the waveform in FIG. 19. With thestructure according to this second embodiment, however, since thecurrent path 66-A is formed as a low-inductance circuit, the voltage ishardly jumped up.

The overall construction of the power converter according to the secondembodiment will be described below.

FIG. 20 is a sectional view showing the construction of the powerconverter INV according to the second embodiment of the presentinvention.

A housing 27 of the power converter INV is made of a material havinggood thermal conductivity and being light, e.g., aluminum, and it has acooling water channel 28 which is formed at a bottom surface of thehousing 27 to cool the whole of the housing 27 and to thermally insulatethe housing interior from the temperature of an external atmosphere. Thepower modules PMU1 and PMU2 generating heat in largest amount withsupply and switching of large currents are arranged nearest to thecooling channel 28 for effective cooling. The capacitor modules CM1 andCM2 are fixed to an inner housing 27-In of the power converter INV byfastening, e.g., screws through the fixing holes 17, shown in FIG. 3,such that upper surfaces of the capacitor modules CM1 and CM2 arecontacted with a lower surface of the inner housing 27-In. With thatstructure, the heat generated from the capacitor modules CM1 and CM2 istransmitted to the inner housing 27-In and is released to a coolantthrough the housing 27 or radiated to the open air through the housing27. The discharge resistance DR serving to discharge charges accumulatedin the capacitor modules CM1 and CM2 is disposed between the capacitormodules CM1 and CM2 and is fixed to the inner housing 27-In in contactwith the lower surface of the inner housing 27-In of the power converterINV. With that structure, during discharge, heat generated from thedischarge resistance DR is transmitted to the inner housing 27-In and isreleased to the coolant through the housing 27 or radiated to the openair through the housing 27.

The driving circuit units DCU1 and DCU2 are arranged above the powermodules PMU1 and PMU2 between the power modules PMU1, PMU2 and thecapacitor modules CM1, CM2, respectively, and the motor control unit MCUis arranged on an upper surface of the inner housing 27-In.

The capacitor modules CM1 and CM2 can be fixed by a manner of formingthreads in the fixing holes, or embedding screws in the molded resin soas to project from it. By thus cooling one surface of each of theresin-molded capacitor modules CM1 and CM2, it is possible to prevent atemperature rise of the capacitor cell CDS caused by the ripple current,and to prolong the useful life of the capacitor cell CDS.

While upper surfaces of the capacitor modules CM1 and CM2 are assumed tobe cooled in this second embodiment, their side surfaces or pluralsurfaces may be cooled by modifying the arrangement of the capacitormodules CM1 and CM2 so as to change the module surfaces connected to thehousing 27 including the inner housing 27-In. Even when the number offixed points is increased with such a modification, stresses applied tothe connecting portions can be moderated in this second embodimentbecause of the presence of the bent structure.

According to this second embodiment, as described above, in avehicle-mounted electrical-mechanical system using the power converterINV to control the two motors MG1 and MG2, capacitors used in the twopower modules PMU1 and PMU2 are constituted by the two capacitor modulesCM1 and CM2 each having a low inductance, and one low-inductancecapacitor module is always combined with one power module, whereby thejumping voltage can be reduced and interference can be avoided. Also,the remaining one capacitor module not connected at a low conductanceserves to increase the capacitor capacity for current supply. As aresult, a size reduction of the power converter INV can be realized.

The construction of a capacitor module according to a third embodimentof the present invention is shown in FIG. 21.

FIG. 21 is an exploded perspective view showing the construction of acapacitor module according to a third embodiment of the presentinvention. Note that, in FIG. 21, the same characters as those in FIG. 4denote the same parts.

In this third embodiment, the basic construction of a capacitor moduleCM is the same as that of the capacitor module CM shown in FIGS. 4-10.However, the U-shaped bent structure, shown in FIG. 4, is not providedin the second flat portion of each of the layered wide conductors 8 and9.

According to this third embodiment, although the effect of moderatingstresses in the connecting portion is not so expected as the caseincluding the bent structure, a certain effect of moderating stressesand reducing inductance can be realized because led-out portions of thewide conductors are in the layered form.

FIG. 22 is a sectional view showing the construction of a capacitormodule according to a fourth embodiment of the present invention.

In this fourth embodiment, the basic construction of a capacitor moduleCM is the same as that of the capacitor module CM shown in FIGS. 4-10.The feature of this fourth embodiment resides in that the direction inwhich the capacitor cell CDS is oriented is changed from the orientationshown in FIG. 4. Because the capacitor cell CDS is fabricated by windinga film which is coated with a metal by vapor deposition, its thermalconductivity is anisotropic. Specifically, the thermal conductivity ishigher in an axial direction CDS-Ax of the wound film than a radialdirection CDS-Rad. Taking into account the above property, in thisfourth embodiment, the axial direction CDS-Ax of the capacitor cell CDSis arranged to face an upper surface of the case 12 so that thecapacitor cell CDS is oriented to ensure more efficient heat conductionat the upper surface of the case 12. As a result, the useful life of thecapacitor cell CDS can be prolonged.

FIG. 23 is a sectional view showing the construction of a capacitormodule according to a fifth embodiment of the present invention.

In this fifth embodiment, the basic construction of a capacitor moduleCM is the same as that of the capacitor module CM shown in FIGS. 4-10.The feature of this fifth embodiment resides in constituting, as oneunit, the capacitor module CM of a power converter in a vehicle-mountedelectrical-mechanical system controlling two motors, while realizingsuch an arrangement that one low-inductance capacitor module can bealways connected to one power module and the remaining one capacitormodule not connected at a low conductance also serves to increase thecapacitor capacity for current supply. The capacitor module CM has astructure wherein a plurality of capacitor cells CDSs are supported oneach of opposite ends of a laminate obtained by bringing two wideconductors into a layered form with an insulation sheet interposedbetween them, and the laminate is connected at its central position tothe power module. That structure eliminates the need of accuratelypositioning two capacitor modules for screwing when those two capacitormodules are assembled. Further, while this fifth embodiment has aplurality of holes formed in a connecting portion of the laminate forconnection to two power modules, the number of the holes formed in theconnecting portion can be reduced and a bottom area can be furtherdownsized when one power module containing the functions of two powermodules is used.

According to the embodiments described above, the capacitor modulehaving a low inductance and being able to moderate stresses in theconnecting portions can be obtained.

Also, according to the embodiments, the power converter INV having asmaller size can be realized.

Further, according to the embodiments, the power converter INV forcontrolling the two motors MG1 and MG2 can be realized in smaller size.

In addition, according to the embodiments, the vehicle-mountedelectrical-mechanical system equipped with the power converter INV forcontrolling the two motors MG1 and MG2 can be realized in smaller size.

1. A power converter comprising: a capacitor module for smoothing DCcurrent supplied from a battery; and a power module having a powersemiconductor device for converting said DC current to AC current in ahousing, wherein the capacitor module comprises: a case having anopening; a plurality of capacitor cells in which first and secondelectrodes are provided on respective end faces, and are arranged in thecase; a first conductor plate which is connected with said firstelectrode; a second conductor plate which is connected with said secondelectrode; and resin which is filled up in the case in order to hold theplurality of capacitor cells, the first conductor plate and the secondconductor plate, wherein the first and the second conductor platesprovide a first portion and a second portion respectively which aredivided through a bending part, the first portions are arranged in thecase, and are connected with the plurality of capacitor cells so thatthe plurality of capacitor cells are in parallel electrically, thesecond portions are extended toward the power module from the opening ofthe case, and are connected with the power module, the opening of thecase faces a face of the power module, and the first and the secondconductor plates include portions bent toward the power module.
 2. Thepower converter according to claim 1, wherein the power module fixes thepower semiconductor device at the face where the capacitor module hasbeen arranged, and provides a base plate which forms the heatdissipation side for radiating heat of the power semiconductor device atthe opposite side while fixing the power semiconductor device.
 3. Thepower converter according to claim 1, wherein the first portion and thesecond portion of the first conductor plate are formed in one, and thefirst portion and the second portion of the second conductor plate areformed in one.
 4. The power converter according to claim 1, wherein eachof the plurality of capacitor cells is a film capacitor wound from afilm, and coated with a metal by vapor deposition, and the electrode isformed on both sides of the wound film in its axial direction by metalspraying.
 5. The power converter according to claim 1, wherein each ofthe plurality of capacitor cells provides a side face and end faceswhich have the electrodes located on both ends of the side face, and theside face faces the bottom of the case, the first portion of the firstconductor plate and the first portion of the second conductor plate arearranged between respective capacitor cells and the opening of the case,the first portion of the first conductor plate provides a plurality offirst electrode connecting portions in which a part of the first portionof the first conductor plate is bent at a position corresponding toarrangement of the capacitor cells, and is connected with one electrodeof the capacitor cells, and the first portion of the second conductorplate provides a plurality of first electrode connecting portions inwhich a part of the first portion of the second conductor plate is bentat a position corresponding to arrangement of the capacitor cells, andis connected with another electrode of the capacitor cells.
 6. The powerconverter according to claim 1, further comprising: through holes thatare formed at the end of the side exposed from resin of the secondportion of the first conductor plate and the second portion of thesecond conductor plate; and screws which are inserted into the throughholes and connect the first conductor plate or the second conductorplate with the power module.
 7. The power converter according to claim1, wherein the case of the capacitor module is rectangular form, andfurther comprising: a power module terminal which provides at least oneof the second portion of the first conductor plate or the second portionof the second conductor plate, is projected from the resin at the end ofthe side which projected from the resin surface of one region of thecase, and is connected with a power module, and a battery terminal whichprovides at least one of the second portion of the first conductor plateor the second portion of the second conductor plate, is projected fromthe resin at the end of another side which projected from the resinsurface of one region of the case, and receives direct current from thebattery.
 8. The power converter according to claim 1, wherein the caseprovides a fixing hole in which a nut for fixing to the housing isburied.
 9. The power converter according to claim 1, wherein the powermodule provides a base plate to which the power semiconductor device isfixed at the face where the capacitor module has been arranged, a powermodule case which is fixed at the base plate, and is formed forsurrounding the power semiconductor, and an external connectingconductor which is pulled out towards the exterior from the inside ofthe case of the power module, and connects with the first conductorplate or the second conductor plate directly, and transmits the directcurrent from the capacitor module to the power semiconductor device. 10.The power converter according to claim 1, wherein a hole is formed in atleast one of the first conductor plate and the second conductor plate,and the first conductor plate or the second conductor plate is supportedat the resin by filling up the resin in the hole.
 11. The powerconverter according to claim 1, wherein a bent portion is formed midwayin a portion extending from the resin toward the direction which thepower module is arranged of the second portion of the first conductorplate and the second portion of the second conductor plate.
 12. Thepower converter according to claim 1, wherein electrodes of at least oneof the plurality of capacitor cells are arranged in a direction reversedfrom a direction in which the electrodes of the other capacitor cellsare arranged.
 13. The power converter according to claim 1, wherein theplurality of the capacitor cells have positive electrodes at a first setof end surfaces thereof and negative electrodes at a second set of endsurfaces and are arrayed on the first conductor plate such thatelectrode direction from the positive electrodes to the negativeelectrodes are substantially parallel to each other in the case to onerow, and the electrode directions of adjacent capacitor cells arereversed from each other.